GB1237356A - Calculator instrument - Google Patents

Abstract

1,237,356. Photographic calculator. MAY & BAKER Ltd. 28 Jan., 1970 [28 Jan., 1969], No. 4590/69. Heading G4B. [Also in Division G2] A deterioration calculator for a photographic bath comprises two relatively movable parts 13, 14 (Fig. 1) and a movable cursor 15, the first movable part 14 bearing a first scale 18 showing the photographic processing speed of the bath, and a second scale 19 graduated similarly to a photographic test strip scale 12 (Fig. 2), and the second movable part 13 bearing a third scale 22 identical with the scale 19 but marked in the reverse direction, and a fourth scale 23 indicating photographic contrast gradient, the test strip 10 (Fig. 2) being differentially exposed along its length to a predetermined extent prior to processing in the bath to be tested, the resulting optical density of the processed strip being measured to find the positions 29, 30 of two particular predetermined optical densities relative to said scale 12, the readings thus obtained being set on the calculator to determine the effective processing speed and the photographic contrast gradient of the bath. The calculator may be in disc form (as shown) or in slide rule or cylindrical form. In the preferred form the member 14 overlies the third scale 22 and is scalloped at the edge to reduce wear. In use the arrow 20 on scale 19 is set to indicate the test strip value corresponding to an optical density of 0À30 on scale 22, and the cursor line adjusted to the test strip value corresponding to an optical density of 3À3 on the scale 19, and values of scales 18 and 23 indicated by the cursor are read off.